We use the perfective will have when we are looking back from a point in time when something will have happened.
By the end of the decade scientists will have discovered a cure for influenza.
I will phone at six o’clock. He will have got home by then.
or looking "back" from the present:
Look at the time. The match will have started.
It’s half past five. Dad will have finished work.
We use would have as the past tense form of will have:
I phoned at six o’clock. I knew he would have got home by then.
It was half past five. Dad would have finished work.
We use would have in past conditionals to talk about something that did not happen:
If it had been a little warmer we would have gone for a swim.
He would have been very angry if he had seen you.